My scenario is to change the number of decimal places through out AX to 4 .It is possible and we can change all the amount fields in AX to 4 decimal places or any no of decimal places.
But the challenge is what will happen to the documents which are in open state or are in progress, for example, open work lines, an open wave, open purchase order lines, open sales order lines, production order at any stage other than ended.
Do this AT YOUR OWN RISK and test everything fully.
Assumption
All open document especially the production orders, work and waves should be closed prior to do this customization.
To change the number of decimal places in Microsoft AX 2012, follow these steps:
1. Change the NoOfDecimals property of the AmountCur, Amount, Qty and RealBase ExtendDataTypes to 4.to do this, follow these steps:
a. Open the Application Object Table (AOT) by pressing CTRL-D on the keyboard.
b. Click Data Dictionary, and then click Extended Data Types.
c. Locate the AmountCur and Qty fields, and then change the NoOfDecimals property to 4.
d. Save the changes that you made in the AOT.

2. Change the round-off value for the exchange rates. To do this, follow these steps:
General Ledger -> Setup -> Currency -> Currency Exchange Rates.
a. Select the Currency -> Click the Round-off tab.
b. Set the round-off value to .0001 on all four modules. These are the following:
∴ General
∴ Sales Order
∴ Purchase Order
∴ Prices

The AmountCur ExtendDataType is used for pricing, and the Qty ExtendDataType is used for quantity amounts. When you change the NoOfDecimals property to 4, all fields and controls that are using these ExtendDataTypes are changed globally. The user can then type values with up to four decimal places.
When you change the round-off value, the value that the user types is saved correctly to the database. Make sure that you add enough zeros for the NoOfDecimals property that you specified. You must make sure to correctly set the NoOfDecimals property so that all four decimal places are used. For example, if you leave the round-off value at .0100, the Net Amount on a purchase order will be rounded to two decimals instead of four.
To make the changes to the decimal place visible for Production sessions and for Master Planning sessions, follow these steps:
1.FOR ax 2009: In the Main Menu window, click Basic, click Setup, click Units, and then click Units.
For ax 2012 Organization Administration -> Setup -> Units -> Units
2. Locate the unit of measure that you want to affect.
In the Decimals field, type 4.
As my scenario was to change all values to 4 decimal places so i have updated all the units listed here to 4 decimal precision
